In the building of the tire, a previously shaped green case composed mainly of a cylindrical carcass band, annular bead cores and bead fillers is arranged on an outer peripheral side of a tire building drum, and a central portion of the green case is expansion-deformed under an action of a building bladder disposed in the tire building drum while approaching both the bead cores to each other under a restraint of the bead cores by this building drum, and then the central portion of the green case is pressed onto an inner peripheral face of a belt-tread band composed mainly of a belt and a tread previously disposed on an outer peripheral side of the drum, and thereafter each end portion of the carcass band is turned around the bead core by double fold bladders disposed adjacent to each end portion of the building bladder and inward and outward in a radial direction.
In order to prevent the retaining of air between the carcass and the bead filler in the above building of the tire, it is proposed that an interior bladder is disposed inside the building bladder and the fold bladders doubly laminated inward and outward in the radial direction are diameter-expanded at a state of diameter-expanding the inner bladder to turn the each end portion of the carcass band, while the carcass band, bead filler and bead core are strongly sandwiched between the interior bladder and an outer fold bladder to remove air between the carcass and the bead filler to thereby enhance the adhesion property therebetween.
According to such a conventional technique, however, the interior bladder is made from a rubber membrane body provided with a reinforcing layer and is relatively low in the rigidity even at the diameter-expanded state, so that the pressing force of the carcass to the bead filler can not be sufficiently enhanced, and hence there is still a fear of retaining air in the bead portion. As a result, there are problems that the uniformity of the product tire may not be held at a good level and in extreme cases, the residual air causes the lowering of the durability in the bead portion.
It is, therefore, an object of the invention to provide a tire building method and a tire building drum wherein the residual air can be sufficiently removed between the carcass and the bead filler in the formation of the bead portion to keep the uniformity of the product tire at a good level and improve the durability of the bead portion.